Prosthodontic seminar ll

vertical jaw relation

Horizontal jaw relation

Shade selection

Pontic size

mounting

• Vertical dimension refers to the length of the face.

• It is maintained either by the

occlusion of the teeth or the

balanced tonic contraction of

the opening and closing

muscles of mandibular

movements.

Vertical jaw relation

Significance

• Provides optimal separation between maxilla and mandible.

• If not measured accurately, the joint will be strained.

• If the VD is altered, severe discomfort to both TMJ and muscles of mastication.

FACTORS AFFECTING VERTICAL DIMENTION

• Tooth : Acts as a vertical stop.

• Musculature : Opening and closing muscles tend to be in a state of minimal tonic contraction.

Vertical dimension of rest

(VDR).

• Vertical separation of the jaws when the opening and closing muscles of mandible are in a state of minimal tonic contraction sufficient only to maintain posture.

Vertical dimension of

occlusion (VDO).

• Vertical separation of the jaws when the teeth or occlusion rims are in contact.

It is generally considered that the teeth should not be in

contact when the jaws are at the vertical dimension of rest

position. The 2 to 4mm distance between the upper and lower

teeth when the mandible is at physiologic rest position is

called interocclusal distance (IOD) frequently referred to as the

“free way space”.

Interocclusal Distance (IOD)

VDR = VDO + IOD

VDR – IOD = VDO

INCREASE IN VDO / DECREASE IN IOD

• The chin-nose distance will increase, and then patients will have an appearance of open mouth.

• Constant pressure to the basal seat area which will lead to bone resorption.

• Soreness of the tissues of the basal seat.

• “Clicking”, of dentures during speech.

• Improper phonetics

DECREASE IN VDO / INCREASE IN IO

• Potentially damaging to the TMJ.

• The normal tongue space is

limited. Facial distortion appears

more noticeable with over

closure

• The muscles of facial expression

lose their tonicity and the face

appears flabby instead of firm

and full.

• Over closure of jaws may lead to

angular chelitis

HORIZONTAL JAW RELATION

Maxillo-mandibular relationship in which the condyles articulate with the thinnest avascular portion of their respective discs with the complex in the anterior superior position against the shapes of the articular eminences.

DEFINITION

TYPES OF HORIZONTAL JAW RELATION

CENTRIC Reference relation with

which the desired occlusion can be coordinated and is constant for each patient, provided that the soft tissue structures in the temporomandibular joints are healthy

ECCENTRIC

Any relationship of mandible to maxilla other than centric relation which include protrusive and lateral relations.

OCCLUSAL RIM Simulate teeth

and help in establishing vertical dimension and centric relation

ORIENTATION OF THE OCCLUSAL PLANE

INTERPUPILLARY LINE CAMPER’S PLANEALAE-TRAGUS LINE

REGISTERING CENTRIC RELATION

Shade selection

Selection of shade

- Color and shade of tooth

The shade consist of:

a. Hue i.e specific color

b. Saturation i.e. amount of color per

unit area.

c. Translucency i.e ability of color to

permit light to pas through it.

Patients age – With

olderage, darker,

while lighter teeth

are suitable for young

patients.

Patients complexion: light teeth

for fair skin, blue eyes, dark

teeth usually for dark skin and

black eyes.

The color should be matched

with the skin of the cheeks

The following facts are true for nearly all natural

teeth:

a.The neck of the tooth has a more pronounced color

than the incisive edge.

b.The incisive edge if not worn, is more transluscent

that the body of the tooth and is usually of a bluish

shade (composed entirely of enamel)

c. The upper central incisors are lightest teeth in the mouth followed

by the laterals and canines. Posterior teeth are usually uniform in

color.

d.Teeth darken slightly with age.

- Aid for selecting the shade

Shade guides – The shade guide tooth should be moistened and

selection made in the normal light.

a.Outside the mouth along the side of the nose.

b.Under the lip with the incisal edge exposed

c. Under the lip with only the cervical end covered and the mouth

open.

Objectives:1.Esthetics2.Masticatory function3.Correction of speech defects4.Preservation of the remaining tissue and

muscle tone

- Primary selection of the teeth must be carried out at the first appointment.

pontic selection

Selection of size (width and length)

a. Size of the face and head

b. Size of the contour of the maxillary arch

c. Maxillomandibular relations

i. In class I – Normal relationship, the teeth in

one arch are compatible with the teeth in the other

arch.

ii. In class II – The mandible is retruded and

the mandibular teeth are frequently smaller

iii. In class III – The mandibular teeth are

frequently larger than normal

Selection of size

Bizygomatic width – The average width of the maxillary central incisor is estimated to be 1-16 of the bizygomatic width that is, the distance between the cheek bones measured just in front of the ears. Some simple devices are available from tooth manufacturers for making this determination or caliper may be used to measure this distance. A face bow maybe used as caliper to make this determination. The combined width of the six maxillary anteriors is slightly less than one third the bizygomatic width.

Width of the anterior teeth

Selection of the form:• Guides for selecting

the form of anterior teeth.

• Shape of the arch.

Posterior teeth selection – Posterior teeth should have a small bucco-lingual width to keep forces on the supporting structure to a minimum.

The mesiodistal measurements of the upper posterior teeth is taken from the distal surface of the canine to the prominence of the tuberosity. The total mesiodistal width of the four posterior teeth is often used as a mould number. The lower posterior teeth should not extend posterior to the mesial border of the retromolar pad.

Posterior teeth selection

Mounting

The master cast must be

accuretly positioned on

an articulator so that

proper occlusion will be

developed during the

tooth arrangment